1. Field of the Invention
The present invention generally relates to match grinding of components of an oil activated fuel injector and, more particularly, to match grinding a spool with a control valve body of an oil activated electronically or mechanically controlled fuel injector.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting or drain ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a control valve of the fuel injector controls the flow of the working fluid from the high pressure supply (known as the rail) to the intensifier chamber and hence the intensifier piston (i.e., fill position), as well as controls the flow of the working fluid from the intensifier chamber to ambient (i.e., drain position). More specifically, a driver delivers a current or voltage to an open side of an open coil solenoid or endcap. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as xe2x80x9cgroovesxe2x80x9d) of the control valve body and the spool. The alignment of the grooves will create a xe2x80x9cfillxe2x80x9d channel which permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). That is, connections to xe2x80x9cfillxe2x80x9d (or xe2x80x9cdrainxe2x80x9d) are established when the edges of the grooves of the spool and the control valve (the open- and close-lands) overlap.
The fill and drain channels must be manufactured within very tight tolerances in order to ensure greater predictability of the fuel injector which, in turn, leads to increased fuel efficiency even at lower fuel quantities. By way of example, once the fill channel is established, the high pressure working fluid acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure begins to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine. If the fill channel is not within prescribed tolerances, the pressure within the high pressure plunger chamber may not be predictable which would negatively affect the action of the needle check valve and hence the fuel efficiency of the fuel injector.
After the injection cycle, the working fluid may be drained to ambient. To provide the drain, a driver delivers a current or voltage to a closed side of a closed coil solenoid or endcap. The magnetic force generated in the closed coil solenoid will shift the spool into the closed position so as to align grooves of the control valve body and the spool. The alignment of the grooves will create a xe2x80x9cdrainxe2x80x9d channel which permits the working fluid to flow from the intensifier chamber of the control valve body to ambient. That is, connections to xe2x80x9cdrainxe2x80x9d are established when the edges of the grooves of the spool and the control valve (the close-lands) overlap. At this time, the intensifier spring will bias the intensifier piston upwards and fuel will then flow into the high pressure plunger chamber to begin another cycle. However, if the drain channel is not within prescribed tolerances, again the predictability of the fuel injector will be adversely affected thereby decreasing fuel efficiency.
With this now understood, it should be well understood that the injector function is strongly influenced by the size of the overlap length of the drain and fill channels. It is the size of these overlap lengths which determines the quantity of working fluid that can flow through the valve for a certain pressure in a certain amount of time. Another important factor in the influence of the injector is the total amount of the spool stroke in the control valve body, i.e., the distance that the spool can travel inside the control valve body from the open to the closed solenoid.
In order to keep the injector function in narrow tolerances, the control valve body and the spool have to be manufactured with very small tolerances. Currently all dimensions for the control valve body and the spool (five dimensions for each of the body and spool), which have an influence on the overlap lengths, are manufactured with a plus/minus tolerance of only a few microns. This translates into ten dimensions with very small tolerances. But, in present manufacturing techniques, spools and control valve bodies are not matched to one another during assembly; that is, after the spools and control valve bodies are manufactured they are then mixed together and assembled without any regard as to whether the assembled components fall within the specified tolerances for the assembled injector. This results in injectors which are not within the specified tolerance range thus negatively influencing the injector performance.
The present invention is directed to overcoming one or more of the problems as set forth above.
In an aspect of the present invention, a method is provided for matching dimensions of a spool to a control valve body of a fuel injector. The method comprises the steps of measuring land locations and an overall length of a first component of the fuel injector and measuring land locations of a second component of the fuel injector relative to at least each other. The method also includes calculating a grinding amount to be removed from the second component based on the following criteria (i) the measured land locations and the overall length of the first component and (ii) the measured land locations of the second component relative to each other.
In embodiments of the first aspect of the present invention, the method further includes measuring a distance between one land location of the land locations and an end of the second component, and an overall initial length of the second component. In further aspects, material is removed from the second component based initially from the measured distance from the one land location relative to the end of the second component and the measured overall initial length of the second component.
In another aspect of the present invention, a method of matching dimensions of a spool with a control valve body of a fuel injector includes the steps of measuring land locations and an overall length of a first component of the fuel injector and measuring land locations of a second component of the fuel injector relative to at least each other. The amount go be removed from one of the components is the calculated based on the measured amounts using a linear optimization process.
In embodiments of the second aspect, the method further includes matching land locations of the first component and the second component based on the calculating step such that the land locations of the first component and the second component and an overall length of the first component and the second component optimize an overlap or alignment between the land locations of the first component and the second component without initial regard to specified tolerances. The first and second components are opened or widened and matched with the other of the first and second components by adjusting fewer than all of the dimensions for overlap length and the stroke of the second component based on the calculating step. The fewer dimensions are preferably eight of ten dimensions which are ground according to the calculating step, and the remaining two dimensions, which are pre-manufactured, are adjusted to the eight dimensions to achieve a desired overlap length and stroke between the first and second components after the calculating step.
In still another aspect of the present invention, a method of matching dimensions of a spool with a control valve body of a fuel injector includes measuring (i) a plurality of dimension of a control valve body including a length and distances from one end to a plurality of land locations and (ii) a plurality of land locations of a spool with respect to one another. The plurality of spool land locations preferably correspond to the plurality of control valve body land locations. Once these dimensions are measured, the method includes calculating a grinding amount to be removed from the spool based on the measured land locations and the overall length of the control valve body and the measured land locations of the spool relative to each other.